The Circulatory System
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The five different types of blood vessels
a. Arteries – Vessel that takes blood away from the heart to arterioles; characteristically possessing thick elastic
and muscular walls. Their walls are composed of three layers (innermost endothelium, middle is smooth
muscle and elastic fibres, and the outer is fibrous connective tissue)
b. Arterioles – Vessel that takes blood from an artery to capillaries
c. Capillaries – Microscopic vessel connecting arterioles to venules; exchange of substances between blood and
tissue fluid occur across their thin walls (only one cell thick)
d. Veins – Vessel that takes blood to the heart from venules; characteristically having non-elastic walls. They
contain valves to prevent backflow of blood
e. Venules – Vessel that takes blood from capillaries to a vein.
Identification and description of major veins and arteries
a. Subclavian arteries and veins – blood vessels that travel under the clavicle (collar bone). The subclavian
arteries are branches of the aorta that take blood to the body walls and shoulder areas. The brachial artery is a
branch of the subclavian artery. The subclavian vein returns blood from these areas to the SVC, which
conducts blood back to the right atrium.
b. Jugular veins – the veins that conduct blood from the head down the neck. They join the SVC allowing the
blood to enter the right atrium.
c. Carotid arteries – a branch of the aorta conducting blood to the head. There is a right and left carotid artery.
They are coupled with the jugular veins that conduct deoxygenated blood away from the head.
d. Mesenteric arteries – the blood vessel that conducts blood to the intestines
e. Hepatic vein – runs between the liver and the IVC
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Hepatic portal vein – vein leading to the liver and formed by merging blood vessels leaving the small intestine
g. Renal vein – vessel that takes blood from the kidney to the IVC
h. Renal artery – vessel that originates from the aorta and delivers blood to the kidney
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Iliac arteries and veins – the major blood vessels of the legs. The dorsal aorta branches to form the iliac
arteries where the iliac veins join together to form the IVC. The umbilical arteries are branches of the iliac
arteries.
Pulmonary Circuit – the portions of the circulatory system that relate to the lunge. The pulmonary circuit begins at the
right ventricle, which pumps blood out of the pulmonary trunk and into the two pulmonary arteries. It includes the
pulmonary capillaries, where external respiration takes place, and the pulmonary veins, which conduct oxygenated blood
to the left atrium.
Systemic Circuit – the part of the circulatory system that delivers oxygenated blood to the body cells. It starts at the left
ventricle and ends at the right atrium.
Differences between adult and fetal circulatory system
Adult
Fetal
 Use of lungs to
 There is a path between the two atria (foramen ovale)
receive oxygen
 There is a path from pulmonary trunk to the aorta (arterial duct), to bypass the lungs
 They do not use their lungs
 They have a placenta and umbilical cord
 Presence of venous ductus, to bypass the liver
Components of blood plasma
a. Water (90-92% of plasma) – maintains blood volumes, transports molecules; absorbed from intestine
b. Plasma proteins (7-8%) – includes albumins, globulins, fibrinogen; maintains blood osmotic pressure, pH,
pressure, volume, transportation, fights infection, and clotting; from liver
c. Salts – (<1%) maintains blood pressure, pH, and aids metabolism: absorbed from intestine
d. Other components include gases (O2 and CO2), nutrients (lipids, glucose, and amino acids), nitrogenous wastes
(urea and uric acid) and other (hormones, vitamins, etc.)
The lymphatic system
a. Lymphatic vessels – vessels that carry lymph
b. Lymphatic capillaries – take up excess tissue fluid called lymph and join lymphatic vessels
c. Red bone marrow – the site of stem cells that are ever capable of dividing and producing blood cells. Site of B
lymphocyte production and maturation
d. Thymus gland – lymphoid organ, located along the trachea behind the sternum, involved in the maturation of T
lymphocytes in the thymus gland. Secretes hormones called thymosins, which aid the maturation of T cells and
perhaps stimulate immune cells in general.
e. Spleen – Large, glandular organ locate in the upper left region of the abdomen; stores and purifies blood
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Lymph nodes – mass of lymphoid tissue located along the course of a lymphatic vessel
Shape, function, and origin of red blood cells, white blood cells, and platelets
Formed elements
Type
Function and Description
Source
Red Blood Cells
Erythrocytes
Red
 Transport O2 and help transport CO2
4 to 6 million per
bone
 7-8 μm in diameter. Bright red to dark purple biconcave disks
mm3 blood
marrow
without nuclei
White Blood Cells Neutrophils
 10-14 μm in diameter. Spherical cells with multilobed nuclei; fine
5-11 000 per mm3 40-70%
pink granules in cytoplasm; phagocytize pathogens
 10-14 μm in diameter. Spherical cells with bilobed nuclei; coarse,
deep-red uniformly sized granules in cytoplasm; phagocytize
-phils are granular 1-4%
antigen-antibody complexes and allergens
leukocytes
Basophils
 10-12 μm in diameter. Spherical cells with lobed nuclei; large
irregularly shaped, deep-blue granules in cytoplasm; release
-cytes are
0-1%
histamine, which promotes blood flow to injured tissues
agranular
Lymphocytes
 5-17 μm in diameter. Spherical cells with large round nuclei;
leukocytes
20-45%
responsible for specific immunity
Monocytes
 10-24 μm in diameter. Large spherical cells with kidney shaped,
All WBCs fight
round, or lobed nuclei; become macrophages that phagocytize
infection
4-8%
pathogens and cellular debris
Platelets
Thrombocytes
 Aids clotting
150-300 000 per
 2-4 μm in diameter. Disk shaped cells fragments with no nuclei;
mm3 blood
purple granules in cytoplasm
Antigen – a substance capable of stimulating the release of antibodies (the immune response). I some cases, antigens
are simply chemical substances (toxins). In other cases, they are cell markers, such as glycoproteins and glycolipids. The
interaction between antibodies and antigens is called agglutination.
Antibody – a class of Y-shaped protein that is released by a type of white blood cell in response to the presence of
foreign antigens. Antibodies bond onto these antigens, causing agglutination.
Capillary-tissue fluid exchange – materials follow their concentration gradient. O2 rich blood cells give O2 to CO2 rich
tissues. They also receive waste. This exchange is relatively easy because capillary walls are one cell thick.
Identify and give functions for
a. Left and right atria – the receiving chambers of the heart. The atria pass blood along o the ventricles to be
pumped out of the heart. They separated from the ventricles be AV valves
b. Left and right ventricle – a chamber. In the heart, the ventricles are the pumping chambers. The left ventricle
marks the beginning to the systemic circuit, where the right ventricle marks the beginning of the pulmonary
circuit.
c. Coronary artery and vein – blood vessels that serve the heart muscle. The coronary artery describes the initial
branches of the aorta going directly to the heart muscle as the aorta ascends out of the left ventricle. Similarly
the coronary vein is actually a set of veins that conduct blood from the heard tissue to the vena cavae as it
enters the right atrium.
d. Superior and inferior vena cava – largest veins in the systemic circuit. The SVC collects blood from the head,
chest, and arms. The IVC collects blood from the lower regions of the body
e. Aorta – the largest artery in the systemic circuit
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Pulmonary arteries and veins – the right and left pulmonary arteries conduct blood to the right and left lungs,
respectively. They are the branches of the pulmonary trunk, which conducts blood out of the right ventricle. The
pulmonary veins conduct blood from the lungs to the left atrium.
g. Atrioventricular valves – large valves made out of connective tissue that allow blood to pass from the atria to the
ventricles of the heart, but not the other way. These valves are closed during systole and opened during diastole.
The AV valves are equipped with chordae tendineae to prevent them from inverting during systole.
h. Chordae tendineae – small tendons which attach the AV valves to muscular extensions from the inside walls of
the ventricles. These tendons prevent the AV flaps from inverting during systole (ventricular contraction)
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Semi-lunar valves – the valves through which blood must pass to exit the heart. As such, there is a semilunar
valve at the beginning of the aorta (called the pulmonary valve). Semi-lunar valves prevent the backflow of blood
into the ventricles
j.
Septum – dividing wall. The heart has a septum that divides the ventricle chambers. In this case, the septum is
the thick muscular wall of both chambers. The Purkinje fibres, which cause the ventricle contractions, run down
the septum.
Sinoatrial (SA) node – one of the two nodes in the heart. These heart nodes are unique in that they are a combination of
nervous tissue and muscle tissue, which allows them to initiate contractions. Both are located in the right atrium. The SA
node is also called the pacemaker of the heart because it is responsible for the intrinsic (unassisted) heart rate of 72
beats per minute. It causes the contraction of the atria and sends an impulse to the AV node to stimulate activity. The AV
node sends impulses down the Purkinje fibres cause the contraction of the ventricles. The SA node is also connected to
the medulla oblongata by both sympathetic and parasympathetic nerve fibres. The sympathetic fibres will increase its
activity, where the parasympathetic will decrease its activity.
Atrio-ventricular (AV) node – one of the two pieces of nodal tissue in the heart. The AV node is under the influence of
impulses from the SA node. It generates impulses that travel through a nerve bundle, down the septum, to a branching
set of nerve fibres, called Purkinje fibres. These innervate the ventricles, thus coordinating their contraction.
Purkinje Fibres – These are nerve tracts that begin at the AV node in the right atrium, extend down the septum of the
heart and out into the massive walls of the ventricles. The ventricular contractions are coordinated because of the
simultaneous delivery of impulses by these nerves.
The SA node and the medulla oblongata automatically control the heartbeat. There are two subdivisions in this autonomic
system, the sympathetic (responses we associate with increased activity and/or stress) and parasympathetic (functions
associated with a resting state).
Blood Pressure: Ideal 120/80 Hypotension 90/60 (or lower) Hypertension 140/90 (or higher). Diet, exercise, disease,
drugs or alcohol, stress, and obesity can affect blood pressure.
Systolic pressure – the force of blood outwards on the arteries when the ventricles are contracting. It decreases with
increasing distance from the heart.
blood
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Eosinophils
19. Diastolic pressure – the pressure that blood exterts outwards on the walls of arteries when the heart is not contracting. It
decreases with increasing distance from the heart.